1. Field of the Invention
The present invention generally relates to an improved method of making cathodes and more particularly a nickel hydroxide - containing cathode for an alkaline battery.
2. Prior Art
It is known that the utilization of active material in a nickel plaque electrode containing nickel hydroxide can be improved by adding cobalt to the electrochemical impregnation (EI) bath during treatment of the nickel plaque. Utilization is defined as the ratio of the capacity, C, observed in the cell utilizing the electrode to the theoretical capacity, C.sub.th, where C.sub.th is the product of active material (g) in the cell times a conversion factor, 0.289AH/g nickel hydroxide. Thus, a nickel plaque can be treated for several minutes in an EI bath containing both cobalt nitrate and nickel nitrate. The nickel plaque is made cathodic in the bath. Nickel hydroxide and cobalt hydroxide are formed in the plaque pores. During a subsequent conversion step in potassium hydroxide electrolyte, the hydroxides are converted to a crystalline structure which accepts a charge. However, the cobalt is not anchored at the sinter surface of the plaque.
A similar improvement in utilization can be obtained by adding cobalt metal powder to the nickel powder slurry during nickel plaque fabrication, to provide a uniform mixture of cobalt and nickel throughout the plaque.
The technique disclosed in Japanese patent JP60-231668 involves the addition of cobalt hydroxide or cobalt oxide to nickel plaque, without the subsequent conversion to cobalt. The hydroxide or oxide is used to protect the plaque surfaces from corrosion.
It is now believed that if cobalt metal could be firmly anchored at the interfacial boundary of the nickel plaque and nickel hydroxide active material deposited in the surfaces of the nickel plaque, an electrode having improved electrical properties could be produced.
Accordingly, there is a need for an improved method of concentrating cobalt metal at the described interfacial boundary in a nickel plaque electrode. Such method should be simple, inexpensive and impart enhanced electrical properties to the electrode. Preferably, the method should be capable of being carried out in several modes to suit individual circumstances.